Conventional cased telescoped ammunition is well known, particularly in connection with larger caliber firing systems. Representative conventional cased telescoped ammunition is disclosed in U.S. Pat. No. 4,907,510 (Martwick et al.), U.S. Pat. No. 4,604,954 (Clarke et al.), U.S. Pat. No. 4,335,657 (Bains), U.S. Pat. No. 4,220,089 (Smith); U.S. Pat. No. 4,197,801 (LaFever et al.), U.S. Pat. No. 2,996,988 (Kunz), and U.S. Pat. No. 2,866,412 (Meyer et al.). The cased telescoped ammunition disclosed in these references have drawbacks, and there is a need for a cased telescoped ammunition round assembly that provides improved performance and reliability.